1. Field of the Invention
The present invention relates to an optical element comprising a plurality of prisms which differ in their refractive indices and to an optical pick-up including the optical element.
2. Description of the Related Art
FIG. 1 is a schematic view of an example of an optical pick-up of the related art.
This optical pick-up 56 comprises a semiconductor laser 4, a collimator lens 5, a beam shaping prism (anamorphic prism) 9, a beam splitter 3, an objective lens 2, and a not shown photodetector.
The semiconductor laser 4 emits a linearly polarized laser beam to the collimator lens 5.
The collimator lens 5 collimates the laser beam from the semiconductor laser 4 to make it a parallel beam directing to the beam shaping prism 9.
The beam shaping prism 9 shapes the laser beam from the collimator lens 5 and emits it to the beam splitter 3.
The beam splitter 3 passes the laser beam from the beam shaping prism 9 and emits it to the objective lens 2.
The objective lens 2 converges the laser beam from the beam splitter 3 and emits it to an optical disk 80 to form a beam spot on the recording surface of the optical disk 80. In addition, the objective lens 2 returns the laser beam reflected from the optical disk 80 (reflected laser beam) to the beam splitter 3.
The beam splitter 3 is struck by the laser beam from the objective lens 2, reflects the incident laser beam by an inner reflecting mirror, and emits it to the photodetector.
The photodetector receives the laser beam from the beam splitter 3 at a receiving unit and generates an output signal.
The output laser beam of the semiconductor laser 4 has a spread angle in the vertical direction different from that in the horizontal direction, so the sectional shape of the output laser beam is elliptical or near elliptical.
The beam shaping prism 9 changes the sectional shape of the laser beam from the semiconductor laser 4 from an ellipse to a circle to make the diameter of the beam in the long axis direction and short axis direction equal or substantially equal. In this way, the beam shaping prism 9 outputs the incident light beam spread in one direction.
FIG. 2 is a schmatic view of the configuration of another example of an optical pick-up of the related art.
This optical pick-up 57 comprises a semiconductor laser 4, a collimator lens 5, a beam shaping prism 39, an objective lens 2, and a not shown photodetector.
The semiconductor laser 4 emits a linearly polarized laser beam to the collimator lens 5.
The collimator lens 5 collimates the laser beam from the semiconductor laser 4 to make it a parallel beam directing to the beam shaping prism 39.
The beam shaping prism 39 shapes the laser beam from the collimator lens 5 and emits it to the objective lens 2.
The objective lens 2 converges the laser beam from the beam shaping prism 39 and directs it to an optical disk 80 to form a beam spot on the recording surface of the optical disk 80. In addition, the objective lens 2 returns the laser beam reflected at the optical disk 80 (reflected laser beam) to the beam shaping prism 39.
The beam shaping prism 39 is struck by the laser beam from the objective lens 2, reflects the incident laser beam, and emits it to the photodetector.
The photodetector receives the laser beam from the beam shaping prism 39 at the receiving unit and generates an output signal.
The output laser beam of the semiconductor laser 4 has a spread angle in the vertical direction different from that in the horizontal direction, so the sectional shape of the output laser beam is elliptical or near elliptical.
The beam shaping prism 39 changes the sectional shape of the laser beam output from the semiconductor laser 4 from an ellipse to a circle to make the diameter of the beam in the long axis direction and short axis direction equal or substantially equal. In this way, the beam shaping prism 39 outputs the incident light beam spread in one direction.
Further, the beam shaping prism 39 also has the function of a beam splitter which reflects the laser beam from the objective lens 2 and directs it to the photodetector.
Note that Japanese Unexamined Patent publication (Kokai) No. 9-80212 discloses an invention of a beam shaping prism and an optical head using the same.
This publication discloses to make the direction of the incident light beam approximately perpendicular to the direction of the emitted light beam by a beam shaping prism having a first prism and a second prism.
In addition, it discloses an optical head which changes the direction of the laser beam from a semiconductor laser (incident laser beam) using the beam shaping prism, sends this laser beam to an optical disk, reflects the laser beam reflected by the optical disk in a direction the same as the incident laser beam by a polarization film, and emits it to a photodetector.
The optical pick-up 56 of FIG. 1 includes a beam splitter 3 and a beam shaping prism 9, so the number of parts rises. This is liable to undesirably lead to higher cost, a larger size, and more complicated production process.
In addition, there is the disadvantage that if the beam shaping prism and/or the beam splitter is tilted, this inclination of the beam shaping prism and/or the beam splitter results in a large change of the optical axis of the laser beam emitted to the photodetector.
Compared with the optical pick-up 56 in FIG. 1, the optical pick-up 57 in FIG. 2 has a beam shaping prism 39 comprising an integrally formed beam splitter 3 and beam shaping prism 9, so it is capable of reducing the number of parts.
There is also the disadvantage that when the beam shaping prism is tilted, the change of the optical axis of the laser beam emitted to the photodetector becomes even larger than the inclination of the beam shaping prism.
A first object of the present invention is to provide an optical pick-up able to reduce the change of the optical axis of the light beam emitted to a photodetector when the beam shaping prism is tilted. A second object is to provide an optical element able to be used in the above optical pick-up.
The first optical element according to the present invention comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having a second refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface, a third prism having the second refractive index and including a third incidence surface in contact with the second emission surface and a first incidence-emission surface forming a fourth angle with the third incidence surface and a third emission surface forming a fifth angle with the third incidence surface, a film between the second emission surface and the third incidence surface and cooperating with the second emission surface and the third incidence surface to emit the light beam striking the third incidence surface from the second emission surface as a first emitted light beam through the first incidence-emission surface, and to emit a second incident light beam striking the third incidence surface from the first incidence-emission surface as a second emitted light beam through the third emission surface. The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface, the first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the change of the wavelength of the incident light beam.
In the present optical element, preferably, the first incident light beam and the first emitted light beam are in the same plane.
Preferably, the plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, the second incidence surface and the second emission surface of the second prism, and the third incidence surface, the first incidence-emission surface, and the third emission surface of the third prism.
In the present optical element, the incidence angle, the first and second refractive indexes, the first angle formed by the first incidence surface and the first emission surface, the second angle formed by the first reflection surface and the first emission surface, the fourth angle formed by the third incidence surface and the first emission surface are defined so that the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
In the present optical element, preferably, the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.5 to approximately 2.2. The second prism may comprise a triangular prism of which the second incidence surface directly intersects with the second emission surface, or may comprise a quadrilateral prism of which the second incidence surface and the emission surface are apart from each other.
The film may comprise a translucent film or a polarization film.
A second optical element according to the present invention comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface forming a second angle with the first incidence surface, a second prism having a second refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface forming a fourth angle with the second incidence surface, a film between the first emission surface and the second incidence surface and cooperating with the first emission surface and the second incidence surface to emit the light beam striking the second incidence surface from the first emission surface as a first emitted light beam through the first incidence-emission surface, and to emit a second incident light beam striking the second incidence surface from the first incidence-emission surface as a second emitted light beam through the second emission surface. The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface, the first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the change of the wavelength of the incident light beam.
In the present optical element, preferably, the first incident light beam and the first emitted light beam are in the same plane.
Preferably, the plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, and the second incidence surface, the first incidence-emission surface, and the second emission surface of the second prism.
In the present optical element, the incidence angle of the first incident light beam, the first and second refractive indexes, the first angle formed by the first incidence surface and the first emission surface, the second angle formed by the first reflection surface and the first incidence surface, the third angle formed by the second incidence surface and the second emission surface, and the fourth angle formed by the second incidence surface and the first incidence-emission surface are defined so that the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
Preferably, the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.5 to approximately 2.2.
The film may comprise a translucent film or a polarization film.
A third optical element according to the present invention comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having the first refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface and forming a third angle with the second incidence surface, a third prism having a second refractive index and including a third incidence surface in contact with the second emission surface and a third emission surface facing the third incidence surface forming a fourth angle with the third incidence surface, a film attached on the third emission surface of the third prism and cooperating with the third emission surface to emit the light beam striking the third incidence surface from the second emission surface as a first emitted light beam, and to reflect a second incident light beam striking the third emission surface and emit it as a second emitted light beam. The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface, the second emission surface and the third incidence surface are defined so as to cancel the change of an optical axis caused by the change of the wavelength of the incident light beam.
In the present optical element, preferably, the first incident light beam and the first emitted light beam are in the same plane.
Preferably, the plane defined by the direction of the first incident light beam and the direction of the the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, the second incidence surface and the second emission surface of the second prism, and the third incidence surface, and the third emission surface of the third prism.
In the present optical element, the incidence angle of the first incident light beam, the first and second refractive indexes, the first angle formed by the first incidence surface and the first emission surface, the second angle formed by the first reflection surface and the first emission surface, the third angle formed by the second incidence surface and the second emission surface, and the fourth angle formed by the third incidence surface and the third emission surface are defined so that the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
In this optical element, preferably, the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.5 to approximately 2.2.
The film may comprise a translucent film or a polarization film.
A fourth optical element according to the present invention comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having the first refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface and forming a third angle with the second incidence surface, and a film attached on the second emission surface of the second prism and cooperating with the second emission surface to emit the light beam striking the second emission surface from the first emission surface as a first emitted light beam, and to reflect a second incident light beam striking the second emission surface and emit it as a second emitted light beam. The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface. The first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the change of the wavelength of the incident light beam.
In this optical element, preferably, the first incident light beam and the first emitted light beam are in the same plane.
Preferably, the plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, and the second incidence surface and the second emission surface of the second prism.
In this optical element, the incidence angle of the first incident light beam, the first and second refractive indexes, the first angle formed by the first incidence surface and the first emission surface, the second angle formed by the first reflection surface and the first emission surface, the third angle formed by the second incidence surface and the second emission surface are defined so that the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam in substantially perpendicular with the direction of the first emitted light beam.
Preferably, the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.5 to approximately 2.2.
The film may comprise a translucent film or a polarization film.
A first optical pick-up according to the present invention comprises an optical element, a light source for generating a light beam to strike the optical element, an objective lens for converging the light beam emitted from the optical element, and a photodetector for detecting the emitted light beam from the optical element. The optical element comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having a second refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface, a third prism having the second refractive index and including a third incidence surface in contact with the second emission surface and a first incidence-emission surface forming a fourth angle with the third incidence surface and a third emission surface forming a fifth angle with the third incidence surface, a film between the second emission surface and the third incidence surface and cooperating with the second emission surface and the third incidence surface to emit the light beam striking the third incidence surface from the second emission surface as a first emitted light beam through the first incidence-emission surface, and to emit a second incident light beam striking the third incidence surface from the first incidence-emission surface as a second emitted light beam through the third emission surface.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface.
The first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the change of the wavelength of the incident light beam.
The optical element is formed so that the first incident light beam and the first emitted light beam are in the same plane, and the plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, the second incidence surface and the second emission surface of the second prism, and the third incidence surface, the first incidence-emission surface, and the third emission surface of the third prism, and the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
The light source is positioned in front of the first incidence surface of the first prism, the objective lens is positioned in front of the first incidence-emission surface of the third prism, the photodetector is positioned in front of the third emission surface of the third prism.
In this optical pick-up the light source is a semiconductor laser that generates the first incident light beam, and the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.9 to approximately 2.1.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle substantially into a light beam having a circular sectioned shape.
The film may comprise a translucent film or a polarization film.
A second optical pick-up according to the present invention comprises an optical element, a light source for generating a light beam to strike the optical element, an objective lens for converging the light beam emitted from the optical element, and a photodetector for detecting the emitted light beam from the optical element. The optical element comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface forming a second angle with the first incidence surface, a second prism having a second refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface forming a fourth angle with the second incidence surface, a film between the first emission surface and the second incidence surface and cooperating with the first emission surface and the second incidence surface to emit the light beam striking the second incidence surface from the first emission surface as a first emitted light beam through the first incidence-emission surface, and to emit a second incident light beam striking the second incidence surface from the first incidence-emission surface as a second emitted light beam through the second emission surface.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface.
The first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the variation of the wavelength of the incident light beam.
In this optical element, the first incident light beam and the first emitted light beam are in the same plane.
The plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, and the second incidence surface, the second incidence-emission surface, and the second emission surface of the second prism.
The direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
The light source is positioned in front of the first incidence surface of the first prism, the objective lens is positioned in front of the first incidence-emission surface of the second prism, and the photodetector is positioned in front of the second emission surface of the second prism.
The light source is a semiconductor laser that generates the first incident light beam, and the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.9 to approximately 2.1.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle substantially into a circular light beam.
The film may be a translucent film or a polarization film.
A third optical pick-up according to the present invention comprises an optical element, a light source for generating a light beam to strike the optical element, an objective lens for converging the light beam emitted from the optical element, and a photodetector for detecting the emitted light beam from the optical element. The optical element comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having the first refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface and forming a third angle with the second incidence surface, a third prism having a second refractive index and including a third incidence surface in contact with the second emission surface and a third emission surface facing the third incidence surface forming a fourth angle with the third incidence surface, a film attached on the third emission surface of the third prism and cooperating with the third emission surface to emit the light beam striking the third incidence surface from the second emission surface as a first emitted light beam, and to reflect a second incident light beam striking the third emission surface and emit it as a second emitted light beam.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface.
The second emission surface and the third incidence surface are defined so as to cancel the change of an optical axis caused by the variation of the wavelength of the incident light beam.
The optical element is formed so that the first incident light beam and the first emitted light beam are in the same plane, and the plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, the second incidence surface and the second emission surface of the second prism, and the third incidence surface, and the third emission surface of the third prism, and the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
The light source is positioned in front of the first incidence surface of the first prism, the objective lens is positioned in front of the first incidence-emission surface of the third prism, the photodetector is positioned in front of the third emission surface of the third prism.
The light source is a semiconductor laser that generates the first incident light beam, and the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.9 to approximately 2.1.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle substantially into a circular light beam.
The film may be a translucent film or a polarization film.
A fourth optical pick-up according to the present invention comprises an optical element, a light source for generating a light beam to strike the optical element, an objective lens for converging the light beam emitted from the optical element, and a photodetector for detecting the emitted light beam from the optical element. The optical element comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having the first refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface and forming a third angle with the second incidence surface, a film attached on the second emission surface of the second prism and cooperating with the second emission surface to emit the light beam striking the second emission surface from the first emission surface as a first emitted light beam, and to reflect a second incident light beam striking the second emission surface and emit it as a second emitted light beam. The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface, the first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the variation of the wavelength of the incident light beam.
The optical element is formed so that the first incident light beam and the first emitted light beam are in the same plane, and the plane defined by the direction of the first incident light beam and the direction of the first emitted light beam substantially perpendicularly intersects the first incidence surface, the first reflection surface, and the first emission surface of the first prism, the second incidence surface and the second emission surface of the second prism, and the direction of the first incident light beam is substantially opposite and parallel to the direction of the second emitted light beam, and the direction of the first incident light beam is substantially perpendicular with the direction of the first emitted light beam.
The light source in positioned in front of the first incidence surface of the first prism, the objective lens is positioned in front of the second emission surface of the second prism along the direction of the first emitted light beam, the photodetector is positioned in front of the second emission surface of the second prism along the direction of the second emitted light beam.
In this optical pick-up, the light source is a semiconductor laser that generates the first incident light beam, and the beam magnification in the plane defined by the direction of the incident light beam and the direction of the emitted light beam is approximately 1.9 to approximately 2.1.
The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle substantially into a circular light beam.
The film may be a translucent film or a polarization film.